MP3384L – 50V, 4-STRING, WHITE LED DRIVER

MP3384L Rev. 1.0

www.MonolithicPower.com

9

12/27/2013

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© 2013 MPS. All Rights Reserved.

APPLICATION INFORMATION

Selecting the Switching Frequency

Set the switching frequency to either 625kHz or

1.25MHz. A bi-level switching-frequency-select

(OSC) input sets the internal oscillator frequency

for the step-up converter. When the OSC pin

connects to GND, the switching frequency is

625kHz. When OSC is left floating or connected

to VCC, the frequency is 1.25MHz.

Setting the LED Current

The LED string currents are identical and set

through the current setting resistor on the ISET

pin.

SET

LED

R

V

.

I

21

1

1000





not leave the ISET pin floating.

Setting Over-Voltage Protection

Over-voltage

protection

(OVP)

implements

open-string protection. In some cases, an LED

string failure results in a feedback voltage of 0V.

The part keeps boosting Vout, until it reaches the

programmed OVP threshold. Then the chip stops

boosting Vout.

To ensure that the chip functions properly, select

an appropriate OVP resistor divider value. The

recommended OVP point is about 1.3 times Vout

for normal operation.

2

2

1

23

1

R

R

R

V

.

V

OVP





PWM Dimming Mode

The MP3384L provides PWM dimming through

an external PWM signal.

Apply a PWM dimming signal ranging from 100Hz

to 2kHz to the PWM pin. The minimum

recommended amplitude of the PWM signal is

1.5V (See Figure 2).

VCC

C1

PWM

MP3384L

PWM Dimming

100Hz~2kHz

Figure 2: PWM Dimming

Selecting the Inductor

A 22μH (for 1.25MHz) or 47µH (for 625kHz)

inductor with a DC current rating at least 40%

higher than the maximum input current is

recommended for most applications. For highest

efficiency, minimize the inductor’s DC resistance.

Selecting the Input Capacitor

The input capacitor reduces the surge current

drawn from the input supply and the switching

noise from the device. The input capacitor

impedance at the switching frequency should be

less than the input source impedance to prevent a

high-frequency, switching current from passing

through the input. Use ceramic capacitors with

X5R or X7R dielectrics because of their low ESR

and small temperature coefficients. For most

applications, a 4.7μF capacitor is sufficient.

Selecting the Output Capacitor

The output capacitor reduces the output voltage

ripple and ensures feedback loop stability. The

output capacitor impedance should be low at the

switching frequency. Ceramic capacitors with

X7R dielectrics are recommended for their low

ESR characteristics. For most applications, a

2.2μF ceramic capacitor is sufficient.